High-gain photodetectors in thin-film transistors fabricated from laser-crystallized silicon on fused silica

We report the achievement of high-gain photoconduction in transistors fabricated in laser-crystallized silicon thin films on fused silica with responsivities of about 300 A/W for radiation in the visible spectrum. Such photodetectors are potentially useful in page-width linear document input scanners with higher speed and resolution than possible with other thin-film sensor arrays. The basic mechanism for photoconductivity consists of spatial separation of photogenerated electron-hole pairs across a p-n junction in the device body, collection of holes in the floating substrate, and ohmic conduction of electrons in a buried channel. This model predicts a long carrier lifetime and is verified by a photocurrent decay time of about 10-100 µs.